Facile preparation of octadecyl monoliths with incorporated carbon nanotubes and neutral monoliths with coated carbon nanotubes stationary phases for HPLC of small and large molecules by hydrophobic and π–π interactions

Abstract

Two approaches for incorporating carbon nanotubes into monolithic columns for HPLC are described in this report. They pertain to the investigation of carbon nanotubes either (i) as entities to modulate solute retention on monolithic columns bearing well defined retentive ligands or (ii) as entities that constitute the stationary phase responsible for solute retention and separation. Approach (i) involved the incorporation of carbon nanotubes into octadecyl monolithic columns while approach (ii) concerns the preparation and evaluation of an ideal monolithic support and coating it with carbon nanotubes to yield a real “carbon nanotube stationary phase” for the HPLC separation of a wide range of solutes. First, an octadecyl monolithic column based on the in situ polymerization of octadecyl acrylate and trimethylolpropane trimethacrylate was optimized for use in HPLC separations of small and large solutes (e.g., proteins). To further modulate the retention and separation of proteins, small amounts of carbon nanotubes were incorporated into the octadecyl monolith column. In approach (ii), an inert, relatively polar monolith based on the in situ polymerization of glyceryl monomethacrylate (GMM) and ethylene glycol dimethacrylate (EDMA) proved to be the most suitable support for the preparation of “carbon nanotube stationary phase”. This carbon nanotube “coated” monolith proved useful in the HPLC separation of a wide range of small solutes including enantiomers. In approach (ii), a more homogeneous incorporation of carbon nanotubes into the diol monolithic columns (i.e., GMM/EDMA) was achieved when hydroxyl functionalized carbon nanotubes were incorporated into the GMM/EDMA monolithic support. In addition, high power sonication for a short time enhanced further the homogeneity of the monolith incorporated with nanotubes. In all cases, nonpolar and π interactions were responsible for solute retention on the monolith incorporated carbon nanotubes.

Nano-Doped Monolithic Materials for Molecular Separation

“…Modulation of protein retention was achieved by varying the amount of MWCNT doped into the monolithic adsorbent. The success of MWCNT-doped monoliths in protein retention was due to the hydrophobic nature and π-π interactions they establish with proteinaceous targets and aromatic amino acid residues [82]. Similarly, an enhancement in separation performance was obtained in the separation of uracil and alkylbenzenes using poly(GMA-co-EDMA-MWCNT) monoliths and poly(GMA-co-EDMA) monoliths modified with MWCNT [83].…”

“…Mayadunne and El Rassi [82] successfully developed multiwalled carbon nanotube (MWCNT) monoliths by means of both copolymerisation and surface modification for the separation and retention of protein molecules. Modulation of protein retention was achieved by varying the amount of MWCNT doped into the monolithic adsorbent.…”

Application of Carbon Nanotubes in Chiral and Achiral Separations of Pharmaceuticals, Biologics and Chemicals

“…This enantioseparation capacity can also be explained by the modification of SWCNTs with carboxylic acid that improves not only their aqueous dispersion but also enhances their enantioseparation. In another experiment, the encapsulation of CNTs in a polymer monolithic column containing GMM and EDMA led to HPLC enantioseparations of a wide range of small molecules [103].The encapsulation of c-SWCNTs in a polymer based monolithic column may also be an appropriate technique for revealing the chirality of CNT. In another experiment, non-carboxylated and ultra-short SWCNTs have been immobilized by non-covalent process into pre-packed HPLC monolithic columns [22].…”

Nanomaterial Fused Monolithic Microcolumns for Biomolecule Separation

“…The presence of boronate on GO has enhanced the dynamic binding capacity of the monolith by 10 fold. To enhance the protein retention and separation efficiency of an octadecyl (C18) monolith (poly ODA-TRIM, (octadecyl acrylate-co-trimethylolpropane trimethacrylate)), Mayadunne and El Rassi [36] incorporated MWNTs into the C18 monolith structure. MWNTs were chosen due to its hydrophobic property and the potential to interact with aromatic aminoacid's (tryptophan, phenylalanine and tyrosine) via π-π bond formation.…”